Click the mouse in the animation region to begin the experiment.

The diagram shows three inverted tubes (barometers) containing mercury. A
sample of water, ethyl alcohol and diethyl ether will be injected into each
barometer. It is OK to view the animation more than once, just click on the
Repeat button.

Important do not press the enter key or the Return key
while you are answering these questions. Your Browser will interpret either
key the same as clicking the mouse on the Submit button. So BE CAREFUL!

Give me some responses to the questions below and I'll give you some extra
credit.

SID#:

Laboratory Section:

1. Before injecting the sample of water into the tube on the left, indicate
what is present (or not present) in the region of the tube above the level
of mercury (labeled with red circle containing the number 1.)

Expert:

Their is a vacuum in the space above the column of mercury, so there are
little if any particles in the vapor phase.

2. Carefully watch what is happening as the sample of water is injected
into the bottom of the tube containing the mercury. Describe what you see
happening. Look for the following; what happens to the first drops of liquid
water as they rise to the top of the mercury column; what happens as more
water reaches the top of the tube; what happens as the last bit of water reaches
the top.

Expert:

When the liquid water is injected at the bottom of the column of mercury,
it moves up the column of mercury because the density of water is less than
the density of mercury. As it moves up the column there is some change but
we'll focus on what happens as it reaches the vacuum at the top of the column.
Initially pressure is very low in the region above the top of the mercury
column, so the liquid water that reaches the top of the column immediately
vaporizes (evaporates) because the pressure due to water is zero. As the water
evaporates the pressure due to water in the vapor phase begins to increase.
The first part of the water sample completely evaporates, and the liquids
continues to evaporate until the pressure due to the water vapor reaches the
equilibrium vapor pressure for water and condensation immediately occurs.
There was enough water injected at the bottom to allow some it to completely
evaporate and for some liquid water to remain.

3. At this point describe what is in the region labeled 2 in the barometer.

Expert:

At this point the region above the liquid water floating on top of the column
of mercury contains water vapor. The pressure exerted by the water vapor can
be determine by measuring the height of the column of mercury and subtracting
that height from the original height of the column before adding the water
sample. The pressure is the equilibrium vapor pressure of water at the temperature
of the room (room temperature).

4. What can you say about the vapor pressure of ethyl alcohol (ethanol)
compare to water at the same temperature?

Expert:

The vapor pressure of the ethyl alcohol is greater than the vapor pressure
of water at the same temperature.

5. What happened to the liquid diethyl ether that was injected into the
barometer? If we measured the height of the column of mercury in the barometer
would that be the vapor pressure of diethyl ether?

Expert:

The initial sample of diethyl ether injected at the bottom of the column
of mercury moved up the column and immediately evaporated. Since the pressure
exerted by the diethyl ether vapor is less than the equilibrium vapor pressure,
all the liquid evaporates. Since there is no liquid present floating on top
of the column mercury at this point measuring the height of the column of
mercury (and subtracting from the original height) gives a measure of the
pressure due to the evaporated diethyl ether, but the measured pressure is
NOT a vapor pressure.

Additional diethyl ether must be added until enough liquid diethyl ether
evaporates so the pressure due to the diethyl ether vapor reaches the equilibrium
vapor pressure....then condensation occurs and we can measure the vapor pressure.

6. What phase(s) must be present to be able to measure the vapor pressure
of a substance in the liquid phase?

Expert:

Both liquid and vapor must be present to measure an equilibrium vapor pressure.

7. Is there anything about this animation that you feel you do not understand?
List your concerns/questions.